1. Field of the Invention
The present invention is directed to ferrite cores in transformers and in particular to the configuration of these cores as related to their functionality.
2. Description of the Related Art
Ferrite cores can be applied in various ways in telecommunications and data technology. Specific material core combinations are required for data transmission standards such as xDSL or ISDN, since the properties of components having ferrite components are essentially dependent on the material and on the core shape of the ferrite core.
For example, ferrite cores are applied as broadband transformers for impedance adaptations, as splitters for separating the speech and data channel (POTS=Plain Old Telephone Service) or as a signal pulse transformer in digital telecommunication networks, in which digital signals or analog signals are transmitted with little distortion. The number of required components is increasingly rising in modem terminal devices of the telecommunication. At the same time, a further reduction of assemblies and modules is desired in order to further reduce the size and weight of the terminal devices and in order to thus improve the handling. Corresponding assemblies and modules therefore have a continuously increasing packing density of the components. It is also desired to increase the packing density by selecting such components requiring less assembly surface on a base, such as a motherboard. Despite the minimization of the component measurements, performance and properties of the components are not to be impaired.
An EP13 ferrite core is currently the standard shape for xDSL transformers. Its behavior is good for a transmission with little distortion, an EP13 core has a beneficial core distortion factor, in particular. It represents a suitable variable for evaluating the distortion behavior and the nonlinear distortion factor. In order to reduce the surface need of the ferrite core, smaller cores than the EP13 core can be used, particularly standard shapes such as EP10 cores and EP7 cores. As a result of the reduced size, these cores also have a smaller middle bleb, which leads to a significantly higher core distortion factor for the component and therefore reduces the performance of the component and its suitability for data transmissions.
An object of the present invention is to provide a new shape for a ferrite core, which has a sufficiently good distortion behavior when the assembly surface is reduced and which has an improved core distortion factor compared to an equally sized core of a standard shape.
The present ferrite core is similar to the standard shaped EP core in that it is composed of two core halves with a parting seam extending vertically to the assembly surface/attachment surface. The present ferrite core represents an intermediate form between an E-core and a shell core. Parallel to the attachment surface and the longitudinal axis, it has a middle bleb flanked by two side parts at both sides. An end piece that is transversely arranged relative to the longitudinal axis of the middle bleb connects middle bleb and side parts such that the bottom edges of middle bleb and side parts are arranged in a plane, which is parallel to the attachment plane. The core has a plane of symmetry vertically residing relative to the attachment plane and comprising the longitudinal axis. In contrast to known EP cores, the inventive ferrite core has a middle bleb with an oval cross-section or flattened oval cross-section, whose longest extent resides vertically to the attachment surface.
In a preferred embodiment of the invention, the inwardly facing surfaces of the side parts follow the oval cross-section or flattened oval cross-section of the middle bleb at a predominately constant distance and form a hollow space for accepting the winding body.
In contrast to a comparable standard shape having the same assembly surface, the performance of the inventive ferrite core is improved. This means that an inventive ferrite core can replace a ferrite core having a larger assembly surface with only insignificant losses given almost equal properties. On the basis of an inventive ferrite core, components allowing a higher packing density can be produced.
The ferrite core can be fashioned as a standard EP core regarding its outer measurements and can have a rectangular base parallel to the attachment plane. The hollow space between the middle bleb and the side parts, which serves the purpose of accepting a coil body with at least one winding, is partially shielded by the side parts. The side parts therefore have a greater height above the attachment plane than the middle bleb. The hollow space formed by the side parts is preferably not completely closed toward the top and has a maximum opening toward the bottom relative to the attachment plane, whereby the opening corresponds to the maximum diameter of the hollow space.
Several advantages are obtained by an inventive ferrite core when the cross-section of the middle bleb is higher and wider. Preferably, the longest diameter of the oval cross-section or flattened oval cross-section, which is vertically oriented relative to the attachment plane, corresponds to at least the 1.2-times of the shortest diameter measured parallel relative to the attachment plane. Inventive ferrite cores can have a middle bleb, whose cross-section has principal axes or, respectively, diameters that differ up to the factor 5.
An inventive ferrite core has a closed magnetic circuit, however, it is divided into two or is fashioned from two core halves that are combined to an overall core along a parting seam in order to facilitate the installation of the coil body or the winding. The complete ferrite core thereby preferably consists of two mirror-inverted halves, whose symmetry plane resides vertically to the attachment plane and vertically to the longitudinal axis. However, it is also possible to divide the ferrite core such that the middle blebs and side parts completely belong to one core half, whereas the second xe2x80x9ccore halfxe2x80x9d is only composed of a further end piece connecting the free ends of the middle blebs and side parts to one another. However, it is also possible to provide the parting seam of the inventive ferrite core at an arbitrary location transverse to the longitudinal axis, whereby core halves of different size arise.
For producing a transformer from the inventive ferrite core, a coil body with preferably two windings is pushed over the middle bleb and the magnetic circuit is closed by joining the two core halves. The coil body can also have fastening pins and contacting pins, which can serve the purpose of connecting the winding ends and of producing the electrical contact with the printed circuit board or with the module substrate. Holding parts such as straps, clamps or caps can assure that the core halves are held together.
The core can be provided with an air gap at the middle bleb or may be formed without an air gap and can be produced from different ferrite materials. The ferrite materials T38, T42, N26 and T55 which are known from the EPCOS data book are particularly preferred for forming cores used in signal transmissions.
The application of inventive ferrite cores, however, it not limited to the transmission of signals. They can also be used as power transformers and are also characterized by their good performance given an improved or, respectively, smaller assembly surface.